The invention relates to a semiconductor device comprising an integrated circuit arranged at a surface of a semiconductor body mainly of the one conductivity type constructed according to an insulated gate field effect device technology, which integrated circuit is provided with a number of output stages for converting signals each having an input for supplying a signal and an output for deriving the transformed signal.
Such a device has been described inter alia in the article "High density frame transfer image sensor", published in "Proceedings of the 14.sup.th Conf. (1982, International) on Solid State Devices", Tokyo, Japan, Journal Appl. Phys., 22, Suppl. 22-1, pages 109-112. This known integrated circuit comprises an image sensor arrangement having a system of charge-coupled devices consisting of an image sensor section, a storage section and a reading section. In the image sensor section, an incident image can be converted into a two-dimensional pattern of charge packets. Subsequently, this pattern can be transferred rapidly to the storage section. While a new image is converted into charge in the image sensor section, the frame stored in the storage section can be read line by line by means of the reading registers.
The reading section comprises three horizontal registers arranged successively in a vertical direction instead of a single register, which is common practice. Thus, as described in the aforementioned publication, the pitch between the vertical registers is not unfavorably influenced by the dimensions of the reading section. In the case of a three-color sensor, it is moreover advantageously possible to use a separate reading register for the three components.
In the known device, the semiconductor body is an n-type silicon substrate, which is provided at the upper surface with a p-type surface region (designated as a "pocket" or "well"). The sensor section, the storage section and the reading registers are constructed according to the n-channel bccd or pccd technology and comprise an n-type surface zone provided in the p-type pocket. During operation, the pn junction between the substrate and the p-type pocket can be biased in the reverse direction. Charge carriers (electrons) generated near this pn junction or in the n-type substrate will be drained via the substrate and therefore will not contribute to the formation of charge packets in the sensor section. Smearing due to electrons which are generated deep in the semiconductor body by the red light and would diffuse to the surface in the absence of this pn junction is thus avoided. Since red and infrared light have a lower absorption coefficient than short-wave light and are therefore absorbed to a higher extent than short-wave light at a larger distance from the upper surface, the sensitivity to red and infra-red light will moreover be reduced and will correspond for red light more accurately to the sensitivity to green and blue light, while the sensitivity to infrared light can be reduced to a very low level.
For reading the charge packets, the outputs of the output registers can be connected to three output amplifiers which are integrated together with the image sensor device in the same semiconductor body. For the manufacture of the amplifiers, the same processing steps are preferably used as for the manufacture of the sensor itself. This may be achieved in that the amplifier is composed of n-channel MOS transistors in a p-type pocket. Due to the comparatively high doping concentration of the p-type pocket, such transistors generally have the disadvantage of a high K factor, which is a measure of the feedback of the pocket voltage to the transistor. This feedback can be reduced by connecting the source to the pocket. In this case, however, it is necessary to form a separate pocket for each amplifier. It has been found that, when at least the output transistors of the amplifier are then constructed in the usual manner, the pitch between the amplifiers becomes larger than the pitch between the output registers. Of course, any distance could be realized between the amplifiers by causing the registers to fan out; however, this configuration would occupy additional space in the semiconductor body and is therefore undesirable.
Such problems may also arise in other types of integrated circuits, more particularly CMOS circuits, which are composed of transistors both of the n-type and of the p-type.